Computation in horizontal models:
For each element (SPEI) or for each node (KSPE) in transient calculations, a storage coefficient S [-] has to be entered for an unconfined aquifer (S = S0 * thickness m).
In confined aquifers, the set specific storage coefficient S0 = S / thickness = 3.3 10-6 [1/m] is used. This set value can be changed during the input dialog of the transient calculation.
In vertical- and 3D models the flow equation as a function of the pressure is used and the storage coefficient is computed using these parameters:
Pressure p,
Saturation Sr,
Density ρ,
flow effective porosity n,
Matrix and fluid compressibility α, β
The default compressibilities of the matrix (α) and the fluid (β) are defined in the input dialog of the transient calculation.
Normally, the assigned porosity n (attribute PORO) is used for the calculation of the specific storage coefficient.
If the module INSTAT is used, the attribute SPEI should be used, since an internal conversion of node (PORO) to element values (SPEI) is not necessary.
If no storage coefficient and porosity are specified, the value 0.2 is used as default value.
Structure of the transient input file